This invention relates to a valve for providing fluid communication between the interior of a tubing string in an oil well and the well annulus surrounding the tubing string. More particularly, the apparatus relates to a circulation valve for use in a testing program for a submerged oil well.
Circulation valves are known for use in a testing program in an oil well wherein the circulation valve opens after a predetermined number of incremental movements. These incremental movements are caused by an increase in annulus pressure wherein the annulus pressure is exerted against a piston to compress an inert gas in the apparatus for supplying a return spring force. Such a circulation valve is disclosed in U.S. Pat. No. 3,850,250 issued Nov. 26, 1974 to Holden et al and assigned to the assignee of the present invention.
Other valves for use in an oil well are known wherein the valves are operated by changing the pressure differential between the pressure in the annulus of the well and that pressure present in a flow channel in the interior of the tubing string.
The use of compressible liquid to provide spring force for use in industrial applications is also known.
A production valve shiftable from one producing formation to another by application of operating pressure changes in the annulus of an oil well is also known as disclosed in U.S. Pat. No. 2,951,536 to Garrett issued Sept. 6, 1960. The valve disclosed therein includes a chamber precharged with gas and a piston dividing the chamber having a metering orifice through said piston wherein pressure increases are metered through said orifice at a predetermined rate to provide a resulting pressure differential between a section of the pressure chamber on one side of the piston from a section of the pressure chamber on the other side of said piston. This pressure differential between chamber sections causes the apparatus to shift from a first position to a second position.
The use of a compressible liquid such as silicon oil, and a mechanical ratchet apparatus for providing for changes in the volume of the compressible liquid as the apparatus is lowered into the well bore is disclosed in a U.S. Patent application to Barrington filed on an even date with the present application and assigned to the assignee of the present invention.
Disclosed is an oil well apparatus for moving a valve in the well bore from a closed position to an open position responsive to sudden changes in the pressure in the well annulus. The apparatus includes a piston arrangement which, when moved a sufficient distance in one longitudinal direction, allows the mentioned valve to be opened.
The piston includes means to balance relatively gradual pressure changes in the well annulus without moving the piston arrangement. Sudden pressure changes in the well annulus will cause an incremental movement of the piston arrangement toward the open position. However, if the sudden pressure change is not followed within a predetermined time with another sudden pressure change, the piston arrangement contains means to return the piston arrangement back to its initial position. It will thus be understood that the piston arrangement is incrementally moved from a position where the valve is closed to a position where the valve is allowed to open by a series of sudden pressure changes where, if the series is interrupted for a sufficient period of time, the piston arrangement will return to its original position.
A piston means is provided having a volume of silicon oil trapped on one side, and subject on a second side to well annulus pressure. Increases in well annulus pressure moves the piston means to compress the silicon oil. A flow metering means is provided in the piston means to allow silicon oil to flow past a piston in the piston means without moving the piston means, thereby allowing for relatively gradual volume changes of the silicon oil as caused by the changing pressure and temperature of the silicon oil as the apparatus is lowered into a well bore.
A spring means is also provided in the piston means for moving the piston means back toward its initial position over a period of time by working in conjunction with the metering means to meter silicon oil flow through the metering means.
A check valve means is also provided for allowing access to the trapped volume of silicon oil at a predetermined point in the well annulus pressure change. In one embodiment, the check valve means is closed when the well annulus pressure is increased, and opens to allow silicon oil out of the trapped volume when a well annulus pressure increase is suddenly released such that the incremental movement occurs in the piston means during pressure increases. In another embodiment, the check valve means opens during a pressure increase to let silicon oil into the trapped volume, and closes during a sudden pressure decrease such that the incremental movement in the piston means occurs when the well annulus pressure is released.
A spring loaded holding means is disclosed to hold the valve in its closed position until the piston means moves a predetermined distance in one longitudinal direction, and then to release for allowing a spring to move the valve to its open position.
The valve disclosed is a well testing circulation valve which is maintained in the closed position during a well testing program, and then opened to allow circulation between the well annulus and the interior of a testing string after a series of well annulus pressure changes within a predetermined time.